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n the last few years important develop-ments and improvements in wort boil-ing technique have been made. Due to

the demand to reduce energy consumptionnew processes and technical solutionshave been introduced in the brewing indus-try. At the same time, however, the follow-ing requirements to achieve optimum beerquality still have to be fulfilled:

❑ stripping of volatile wort aroma compo-nents;

❑ coagulation of protein fractions;❑ isomerization of hops and hop products;❑ no oxygen pick-up during the boiling

process;❑ efficient hot break separation in the

Whirlpool.

Optimum results in terms of brewing andenergy technology require a comprehen-sive consideration of all process steps ofwort boiling. The following paper explainsHuppmann’s understanding of modernwort boiling as a package consisting ofheating-up, the actual wort boiling andwort treatment during cast-out.

■■■■■ Wort heating to boiling temperature

In the conventional process the lauteredwort is transferred to the wort kettle with atemperature of approx. 72 – 74 °C and heat-

ed up there. During heating-up, however,wort with this temperature is continuouslyentering the wort kettle. This leads to aninhomogeneous temperature distributionin the kettle. Wort with a different tempera-ture enters the lower end of the internalboiler. The “colder” wort disturbs the ther-mal balance in the boiler tube, which re-sults in an interruption of the upward flow.

This interruption in the process can beobserved in many wort kettles with inter-nal boilers and is well known among brew-ers as “pulsation” of the internal boiler.This phenomenon can be avoided by tak-ing the following measures in the heatingprocess in the wort kettle:

1. Forced flow into the internal boilercaused by a centrifugal pump creatingconsistent and adjusted flow ratesthrough the internal boiler according toa patented procedure (1).

2. Wort preheating in a plate and frameheat exchanger, which is either– steam-heated (risk of coagulation ofprotein fractions due to high wall tem-peratures) or better– hot-water heated (preventing unde-sired coagulation).

In brewing plants with an energy storagesystem (Fig. 1), water with a temperature ofapprox. 96 – 98 °C from the energy storagetank (circuit water) is heated up to approx.101 °C by means of steam in a second plateand frame heat exchanger (“Booster heatexchanger”). This hot circuit water nowheats up the wort very gently to almostboiling temperature. With water as heattransfer medium the wall temperatures onthe wort side remain safely below the boil-ing point and undesirable protein precipi-tation reactions are reduced considerably.This procedure does not affect the hot wa-ter balance of the brewery, as the water isled in a closed circuit back into the energystorage tank again with a temperature ofapprox. 78 – 80 °C. Up to a total evaporationof just under 5 %, the energy recoveredfrom the vapours during boiling can thus

Dynamic low-pressure boiling –systematically optimized for top quality

Authors: Dr. Thomas Bühler, Rudolf Michel,Bernd Kantelberg, Yvonne Baumgärtner,Huppmann Group, Kitzingen, Germany

Th. Bühler, R. Michel, B. Kantelberg, Yvonne Baumgärtner, Kitzingen

Optimum results in termsof brewing and energytechnology require a

comprehensiveconsideration of all

process steps of wortboiling. Therefore

Huppmann understandsmodern wort boiling as a

package consisting ofheating-up, the actual wortboiling and wort treatment

during cast-out. Acomparison of different

systems proves theadvantages of this global

approach.

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be used completely for wort preheating.During the start-up of a brewing line, thesteam-heated “Booster heat exchanger”can also be used to heat up the energy stor-age tank, which has slightly cooled downduring the shut-down time.

In breweries which do not have an ener-gy recovery system hot water from an 80 °C

hot water tank can be used, analogous tothe procedure described above (Fig. 2).The water from the 80 °C tank is also heat-ed up to approx. 101 °C in the steam-heated“Booster heat exchanger” and is led backto the tank with a temperature of approx.80 °C after wort heating. So this processvariant does not affect the hot water bal-ance of the brewery either.

With the integration of this gentle wortpreheating process, “pulsation” of the in-ternal boiler can be reliably avoided in allinternal boiler plants. The reduction ofthermal stress on the wort contributes tothe preservation of the foam-positive pro-tein fractions in the wort already in thisphase. Due to the very even temperaturedistribution in the wort kettle near boilingtemperature, intensive boiling with veryintensive wort distribution over the two-level wort spreader is achieved immediate-ly (2).

■■■■■ Dynamic low-pressure boiling (LPB)

A lot of geometric parameters have to betaken into consideration for designing thekettle, the internal boiler and its cone andthe 2-level wort spreader and its position inthe kettle.

In the course of the research work onvolatile stripping, Huppmann developedthe classic spreader – often referred to as“Chinaman’s hat” – to a patented two-levelwort spreader, which throws the wort backon the wort surface in two different levels(3). This leads to improved scrubbing ofundesirable aroma components from thewort. Another target to be achieved withthe design of the outlet cone on the internalboiler and the wort spreader is to create apiston flow in the kettle during the atmos-pheric boiling phases (like e.g. pre- and af-ter-boiling, if dynamic LPB is used). Due tothis intensive boiling movement during at-mospheric boiling the kettle content wouldbe circulated approx. 20 times within onehour boiling time.

The plant configuration described in thefollowing in combination with an opti-mized low-pressure boiling process allowsa considerable shortening of the boilingtime and a reduction of the evaporation

Fig. 1 Wort preheating with energy storage tank and“Booster heat exchanger”

Fig. 2 Wort preheating with 80 °C hot water and “Boosterheat exchanger”

Fig. 4 Totalevaporationin differentboilingsystems(Source: seeFig. 3)

Fig. 3Coagulablenitrogen –behaviour indifferentboilingsystems

Source: Internal boiler and “heated cone”, data presented in (6); internalboiler “new”, data presented in (7); mechanical vapour recompression(MVR) with wort precooling (PC) to 94 °C (Huppmann test series 243);dynamic low-pressure boiling (LPB) with wort precooling (PC) to 89 °C,(Huppmann test series 279)

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rate including positive impacts on beerquality. The process of dynamic low-pres-sure boiling is divided into three mainsteps:

1. Short atmospheric pre-boiling servingthe purpose of deaeration of the wortkettle, the pressure regulation systemand the vapour condenser

2. Defined pressure build-up in the wortkettle and deliberate pressure release –repetition of this process up to approx.15 times (depending on e.g. the raw ma-terial quality)

3. Atmospheric after-boiling to achieve thedesired cast-out wort concentration

The flow rate through the vapour con-denser and a control valve installed as abypass around the vent stack valve areused to reach the pressure setpoint of e.g.150 mbar within a given time interval. Theenergy supplied via the internal boiler isused to achieve the requested pressurepeaks and to heat up the wort to a temper-ature of approx. 102 – 103 °C.

When the set pressure has beenreached, deliberate pressure reductionstarts immediately. Under defined condi-tions and with a specified reduction rate∆p/∆t, the pressure in the wort kettle is re-duced to e.g. 50 mbar. With the pressurereduction, the corresponding boiling tem-perature in the kettle goes down and steambubbles are rapidly produced in the entirekettle content. This intensive boiling proc-ess causes a perfect stripping of volatilesdue to the very big gas/liquid interface.This makes the difference between dynam-ic LPB and other boiling methods. In thecase of atmospheric boiling with internalor external boiler or also in the case of boil-ing methods with double-walled heatingcones only the temperature of the wortwhich is in contact with the heating surfacerises to or slightly above boiling tempera-ture.

Bursting of the steam bubbles on theentire vessel surface improves the strip-

ping of the undesirable flavour compo-nents as well as the agglomeration of hotbreak particles to bigger units. During hotbreak separation in the Whirlpool thisleads to the formation of a compact trubcone, which ensures draw-off of a clearwort with little solids content. In case ofboiling systems with continuous forcedflow into the internal boiler caused by acentrifugal pump, however, the formedprotein agglomerates are destroyed. Thisimpairs the Whirlpool performance con-siderably.

The rising steam bubbles cause someprocess-related foaming. The more inten-sive this process is, the better the stripping

Fig. 5Dynamiclow-pressureboiling withfractionalheating

of the undesirable aroma and aging compo-nents. As the internal boiler is also workingduring the pressure release step, the wortsprayed down from the spreader destroysthe foam in the wort kettle and improvesthe evaporation performance at the sametime.

This dynamic process “energy supplyand pressure build-up“ – “pressure releasewith flash evaporation” can be repeated upto 15 times in order to adjust – besides theother wort parameters – e.g. also the coag-ulation and protein precipitation. Fig. 3shows the comparison of different boilingsystems in this connection. The values aretaken from various current publicationsand from Huppmann test series.

In the last release step the vessel or re-lease pressure is reduced to atmosphericpressure again. The next step, atmospheric“after-boiling”, is important to achieve therequired cast-out wort concentration. Withthis procedure, boiling times of 40 – 50 min-utes can be realized and total evaporationrates of 3 – 5 % can be adjusted. Figure 4shows the total evaporation of the com-pared boiling systems.

In the course of development projects atHuppmann in the field of wort boiling a newprocess variant of dynamic LPB was estab-lished (see Fig. 5). The fractional heating

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used in this connection leads to furtherimprovements, for example foaming due tothe raw material is consistently avoided.Hop isomerization in case of early hop dos-ing is accelerated and despite little energysupply the reactions desired in the boilingprocess are reliably realized.

■■■■■ Wort precooling – a simple methodto reduce free DMS in the Whirlpoolwort

The DMS content in the final productdepends on the DMS-precursor content inthe raw materials, the mashing processand the efficiency and the parameters ofthe boiling method. During wort boilingthere is a constant transformation of theDMS-precursor to free DMS in the wort. Thefree DMS is stripped off with the vapour.

With the end of the boiling process theremoval of free DMS by volatile stripping isstopped, while the transformation of theDMS-precursor to free DMS continues. It isonly possible to influence the DMS concen-tration in the final product with additionalequipment like stripping columns undervacuum or thin layer evaporators with bigsurfaces. Considering that the velocity ofthis reaction depends on the temperatureof the wort, a very simple but effectivetechnique to suppress this reaction wasdeveloped: the reduction of temperature

between the cast-out procedure and theWhirlpool rest from boiling temperature toapprox. 89 °C using a separate plate andframe heat exchanger or using the usualwort cooler for a partial wort flow. In thisway, the additional formation of DMS is re-duced by approx. 30 %, the TBA increasewill be reduced by approx. 20 %. Furtherdetails on DMS and TBA figures have al-ready been published by Coors et al. (4).

■■■■■ Comparison of quality criteria:Thermal stress and free DMS

Figures 6 and 7 show the impact of differ-ent boiling methods on the development offree DMS and compounds that are formeddue to thermal stress. This thermal indica-tor substances are recorded as thiobarbi-turic acid figure (TBA) (5). The data arefrom four different breweries having differ-ent raw material qualities and wort compo-sitions. This explains the different initialvalues of free DMS in the kettle-full wort aswell as the high initial value of TBA at thestart of the boiling process (“kettle full”) inthe series of tests with dynamic LPB.

The two variants of internal boilers, me-chanical vapour recompression and dy-namic low-pressure boiling show a similarbehaviour: Reduction of free DMS from“kettle full” to “cast wort” and increase dur-ing the Whirlpool rest. The system with

heated cone requires an additional strip-ping stage after the Whirlpool rest toachieve lower values in the cold wort.

Apart from the absolute values, Fig. 7also shows the increase of the TBA per-centage of these particular boiling meth-ods in the boiling phase from “kettle full” to“cast wort”. The percentage increase im-pressively shows that vapour recompres-sion with its lower steam pressure (and theassociated lower heating surface tempera-ture) has a very slight increase of TBA by69 % during boiling. Dynamic low-pressureboiling with wort preheating has the leastthermal stress of all mentioned systemswith an increase by only 28 % during boil-ing. The maximum thermal stress occurs ifonly an internal boiler is used for heating-up and for wort boiling. The exampleshows an increase of the TBA figure by 81 %in case of “internal boiler” and in case of“internal boiler new” even by 105 %.

■■■■■ Conclusion

Dynamic low-pressure boiling as a sys-tematically optimized wort boiling methodprovides a lot of parameters to influencewort quality and energy costs: Heating-up,preboiling phase, number of pressurepeaks, temperature level, atmospheric af-ter-boiling and wort precooling.

Due to its high flexibility this techniquecan be adjusted to all kinds of different re-quirements, no matter if they are a result ofthe raw materials used or of the brewery’sdemand for energy savings. Every systemdescribed here can be installed individual-ly or be retrofitted in existing brewhouses.A comparison with other boiling systemsbased on the key quality parameters con-firms the efficiency of the system.

■■■■■ Summary

In order to meet the demands of thebrewing industry regarding beer qualityand energy saving, Huppmann is systemat-ically working on the improvement of wortboiling technology. The brewhouse plantmanufacturer has developed an effectiveand flexible but simple concept to fulfil allrequirements of the breweries. These con-tinuous optimization included geometricalmodifications at the internal boiler and thewort spreader as well as process modifica-tions and improvements in the boilingprocess itself. External preheating with anenergy storage system allows to heat upthe wort nearly to boiling temperature be-fore it enters the wort kettle. This specialprocedure avoids pulsation of the internalboiler and thus contributes to the preser-vation of protein components which have apositive impact on foam development.There are some alternatives for breweries

Fig. 6 Behaviourof free DMS in thecompared boilingmethods (Source:see Fig. 3; value forinternal boiler“new” at themiddle of thecooling processnot available)

Fig. 7 Thermalstress (TBA) inthe comparedboiling methods(Source: see Fig.3; value forinternal boiler“new” at themiddle of thecooling processnot available)

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without energy storage system, e.g. forcedflow into the internal boiler caused by acentrifugal pump at the beginning of theheating process, a measure that was firstrealized by Huppmann.

The article documents the latest devel-opments in dynamic low-pressure boilingfor wort production based on current re-sults from industrial plants. It comparesthe essential qualitative variables meas-ured, like coagulable nitrogen and dimeth-ylsulphide (DMS) and the thiobarbituricacid figure (TBA), with the results of othermodern boiling systems. The comparisonshows that dynamic low-pressure boiling

as a very gentle boiling method achieves avery good product quality in all aspectswith a total evaporation rate between 3 – 5% and short boiling times of 40 – 50 minutes.

■■■■■ Literature1. Höfig, Heinz, Würzepfanne mit Innenkocher

und Umwälzpumpe. German Patent (1994), DE4304 383.

2. Michel, R. und Kantelberg, B., Reduction ofWort Thermal Stress Relative to heating Meth-ods and Wort Treatment. MBAA TechnicalQuarterly 39, (2002), No. 3 P.156-164.

3. Michel, R.; Vollhals, B.: Dynamic Wort Boiling.MBAA Technical Quarterly 40 (2003) No. 1, P.25-29.

4. Coors, G., Krottenthaler, M., Back, W.,Auswirkungen einer Würzevorkühlung beimAusschlagen, Brauwelt 140 (2000), No. 42/43,P. 1696-1699.

5. Birkenstock, B. Anwendung der Thiobar-bitursäurezahl (TBZ) in der brautechnischenBetriebsüberwachung, Brauwelt 130, (1990),No. 3, P. 44-46.

6. N.N. Handouts to the presentation of the Kro-nes Group, Hotel New World, Ho-Chi-Minh-City, Vietnam, 30.10. - 01.11.2002.

7. Wasmuht, K., Stippler, K., Weinzierl, M., Gat-termeier, P., Stromboli kocht ohne Druck –eine sympathische Lösung, Brauwelt 143,(2003), No. 30, P. 949-952.

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Re-published with kind permission of the Copyright Owner: Fachverlag Hans Carl, Nürnberg